Drop unused dependency

Summary:
It was introduced with c99775ef3cfe7c9c5718d73a1dc2fef8cde69a34 but
I couldn't find why or any usage.

Test Plan: Builds and installs the same content as before

Reviewers: Plasma

Subscribers: plasma-devel

Tags: Plasma, Kirigami

Differential Revision: https://phabricator.kde.org/D7239